The United States government has certain rights in this invention by virtue of a grant from the National Institutes of Health NIDDKD to James R. Goldenring.
Gastric cancer worldwide is the second highest cause of death from cancer. While rates of gastric cancer have been decreasing in the United States, gastric cancer prevalence remains high in other parts of the world, especially in Asia. Presently, patients in endemic regions for gastric cancer, especially Japan and China, undergo screening by upper endoscopy. There is no alternative at present for discovery of early cancer other than by endoscopy. Grading of these endoscopies is based solely on hematoxylin and eosin staining. There are no prognostic markers that could indicate those at risk for future cancer development. Therefore, while biopsies can reveal early gastric cancers, patients in high risk regions who are initially negative by endoscopy must be followed with endoscopies to rule out future developments.
The epidemiological association between chronic H. pylori infection and gastric carcinoma is now well established, such that the Working Group Meeting of the International Agency for Research on Cancer with the World Health Organization recently classified Helicobacter pylori as a group 1 human gastric carcinogen (Peura, D. A. Gastroenterology 113, S4-S8 (1997)). Parsonnet and colleagues reported that 84% of patients with gastric cancer had serum antibodies against H. pylori, as opposed to 66% of uninfected matched controls (Parsonnet, et al. New Eng. J. Med. 325, 1127-1131(1991)). H. pylori infection induces a chronic gastritis progressing to atrophic gastritis, foveolar hyperplasia and intestinal metaplasia (Mobley, H. T. L. Gastroenterology 113, S21-S28 (1997)). Recent studies have indicated that chronic gastritis associated with Helicobacter pylori contributes to the development of gastric adenocarcinoma (Peura, D. A. Gastroenterology 113, S4-S8 (1997); Parsonnet, et al. New Eng. J. Med. 325, 1127-1131 (1991); Forman et al. Br. J. Med. 302, 1302-1305 (1991); Normura, et al. New Eng. J. Med. 325 1132-1136 (1991)). Nevertheless, the mechanism of progression from chronic gastritis to malignant disease remains unclear, and the relationship of intestinal metaplasia, H. pylori infection and the development of cancer continues to be controversial. Moreover, while an association between gastric cancer and infection with H. pylori has recently been established, the cell of origin for gastric adenocarcinoma is controversial. This does not establish a mechanism between the bacteria and the cancer, and provides little or no guidance for correlating treatment of, or risk associated with, H. pylori as it relates to development of gastric cancer.
It is therefore an object of the present invention to provide screening methods for early gastric cancer.
It is a further object of the present invention to provide means for assessing the degree of early gastric cancer and for screening and following patients at risk for gastric cancer.
It is a still further object of the present invention to provide means for serological testing for patients at risk of gastric cancer.
It has been determined that a specific metaplastic lineage that contains immunoreactivity for a trefoil polypeptide, spasmolytic peptide, is associated with and gives rise to the vast majority of human adenocarcinomas. The identification of this Spasmolytic Polypeptide Expressing Metaplasia (SPEM) is a major factor for grading of biopsies of the stomach to assess risk for gastric cancer. It also forms the basis of a method for serological screening for those at risk for gastric cancer. In a preferred embodiment, antibodies to spasmolytic peptide (hSP) are used in immunostaining of biopsies of gastric tissue obtained by endoscopy for grading biopsies. Those patients having these cells, characterized by a morphology more typical of a type of cell present normally in the intestine and not stomach, Brunner""s gland cells, are at risk of developing adenocacinoma. Since these cells express hSP, antibodies or nucleic acid probes hybridizing to mRNA encoding hSP, can be used for rapid detection of the cells in tissue biopsies. The antibodies can also be used in serological tests for screening and following patients at risk for gastric cancer. In combination with evidence of previous or present invention with H. pylori, the tests are predictive of the likelihood of developing adenocarcinoma.
Metaplastic cell lineages arising in response to chronic injury are precursors for the evolution of dysplasia and adenocarcinoma. This sequence is well characterized in the case of the Barrett""s epithelium, a columnar specialized intestinal metaplasia in the distal esophagus of patients with esophageal reflux (Haggitt, R. C. Hum. Pathol. 25, 982-993 (1994)). While a subtype of intestinal metaplasia has been associated with gastric adenocarcinoma (Dixon, et al. Am. J. Surg. Pathol. 20, 1161-1181 (1996); Filipe et al. Int. J. Cancer. 57, 324-329 (1994)); Correa, P. Cancer Res. 48, 3554-3560 (1988)), the link between these lineages and the evolution of gastric adenocarcinoma has not been clear. It has now been determined that there is an association between SPEM, detectable in biopsies based on the presence of cells having a morphology similar to Brunner""s gland cells, and adenocarcinoma. Although normal cells in the stomach, such as mucus neck cells, express hSP, these cells are not predictive of adenocarcinoma.
A. Histology of the Gastric Tissues
Presently, gastric mucosal biopsies are fixed in formalin and embedded in paraffin. Microtome sections of tissues are then stained with hematoxylin and eosin. These stained slides are examined for loss of parietal cells (oxyntic atrophy), ulceration, inflammatory infiltrates, and alterations in cell lineages including increased numbers of surface mucous cells (foveolar hyperplasia), the presence of goblet cells (intestinal metaplasia), as well as dysplasia and adenocarcinoma. Dysplasia and adenocarcinoma are judged by changes in nuclear morphology, loss of cytoplasmic space, loss of polarity and invasion of submucosa or vasculature. Brunner""s glands are not present in the normal stomach but can be observed in the duodenum.
B. Markers of SPEM
Small peptides displaying a cysteine-rich module (termed P-domain or trefoil motif) form a group of peptides, including BCEI, expressed from the pS2 gene; hITF, expressed from the TFF3 gene; and hSP, expressed from the SML1 gene. These peptides are abundantly expressed at mucosal surfaces of specific tissues and are associated with the maintenance of surface integrity. (Schmitt, et al., Cytogenet. Cell Genet. 72(4), 299-302 (1996)). Human spasmolytic peptide (hSP) was identified by Romasetto, et al., EMBO J., 9(2), 407-414 (1990), based on homology to pancreatic spasmolytic polypeptide, sequenced and determined to be separately encoded on the genome from pS2. The gene sequence and amino acid sequences of hSP can be obtained from GenBank, accession number 1477545. Both are present in normal stomach epithelium. The patterns and timing of the expression of the trefoil peptides are different from each other. It is thought that S2 plays an important role in the proliferation of intestinal epithelial cells during the acute phase of mucosal ulceration, whereas ITF may be involved in differentiation of the cells, particularly to form goblet cells, during the recovery phase of acute colitis. (Itoh, et al., Biochem. J. 318(Pt 3), 939-944 (1996)). Immunostaining for SP in the intact mucosa has been determined to be confined to the mucous neck cells, but following exposure to stress it was significantly enhanced and occurred also in the cells of the basal region of gastric glands, as reported by Konturek, et al., Regul. Pept. 68(1), 71-79 (1997). Konturek, et al. (1997) proposed that SP plays an important role in healing of stress-induced gastric lesions, possibly by the acceleration of the mucosal repair, the enhancement of mucosal blood flow and the inhibition of gastric secretion.
It has now been determined that SP is a marker of metaplastic cells having a morphology similar to those of Brunner""s gland cells. These cells can be identified by histological examination. However, the identification of SPEM with spasmolytic peptide immunostaining is easier, more sensitive and rapid. Therefore, detection of metaplastic cells expressing SP provides a means for identification of those at risk who would need further follow-up. Furthermore, since the SPEM lineage is often extensive, quantitation of serum spasmolytic polypeptide levels by either radioimmunoassay or ELISA should be useful to stratify patients at risk and provide a serological method for identifying and following patients at risk for developing adenocarcinoma.
SPEM can be detected using antibodies or antibody fragments prepared by standard techniques. The studies described in the examples were performed with a mouse monoclonal IgM anti-human spasmolytic polypeptide developed by Drs. Richard Poulsom and Nicholas Wright at the Imperial Cancer Research Fund, London, UK. Antibodies specifically directed towards utility in RIA and ELISA have also been developed. Either monoclonal or polyclonal antibodies can be used. Antibodies can be labelled using any detectable marker, including radiolabels, fluorescent labels, dyes, enzyme-chromogenic substrate systems, and other means commercially available.
SPEM can also be detected using nucleic acid probes which hybridize under standard hybridization conditions, as described for example, by Maniatis, et al. Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory), to mRNA encoding SP. These can be labeled using standard labelling techniques for detection of bound nucleic acid.
Alternatively, or in addition, other markers of these cells can be used to screen for the presence of SPEM in gastric tissue biopsies.
For serological assay of SP, serum would be obtained from fasting patients. SP levels would be determined using either radioimmunoassay or enzyme-linked immunoassay. A standard curve would be used for known amounts of recombinant SP (Lars Thimm, Novartis Corporation). Patients with elevated levels of SP in serum would be investigated for the presence of SPEM by endoscopy. Alternatively, patients with elevated serum SP and documented SPEM could be followed following treatment of H. pylori by serial serum determinations of SP.
C. Detection of H. pylori Infection
Since H. pylori is known to be associated with an increased incidence of adenocarcinoma of the stomach, efficacy of screening can be further enhanced by testing for previous or present H. pylori infection. H. pylori infection would be determined by either CLO test at the time of biopsy or H. pylori serology with the same sample used for SP determination.
SP detection, such as immunohistochemistry, can be used to determine the presence of SPEM in endoscopic biopsies as well as brushings obtained either through endoscopy or blind per oral intubation.
As noted above, gastric cancer screening, especially in Asian 25 countries, is a major focus for clinical care. Presently, the only impact of medicine on gastric cancer is through early detection of low grade tumors and early resection for cure. High grade tumors have uniformly dismal prognosis with median survival less than one year. No significant effect of adjuvant chemotherapy has been noted. The addition of spasmolytic polypeptide immunostaining of biopsies and the identification of SPEM provides a means for identifying those at risk for developing cancer in the future. Similarly, the use of spasmolytic peptide serology should provide a blood test for identification of those at risk. Thus, the use of spasmolytic polypeptide immunostaining could significantly decrease the number of screening endoscopies, focus screening endoscopies, and, through serology testing, facilitate screening of large populations a risk in Asia and other countries with high cancer incidence.
The present invention will be further understood by reference to the following non-limiting examples.
Wang and colleagues examined the influences of chronic Helicobacter gastritis using Helicobacter felis to infect the gastric epithelium of C57BL/6 mice (Wang, et al. Gastroenterology. 114, 675-689 (1998)). Infection with H. felis produced a chronic gastritis with pathologic features similar to human infection with H. pylori including marked loss of parietal and chief cell populations, in addition to elaboration of an aberrant mucous cell lineage (Lee, et al. Gastroenterology. 99, 1315-1323 (1990); Fox, et al., Gastroenterology. 110, 155-166 (1996)). Wang, et al. (1998) reported that an aberrant metaplastic cell lineage with morphological characteristics similar to Brunner""s glands of the duodenum develops in the fundic mucosa of mice infected with H. felis. This metaplastic lineage expresses the trefoil peptide spasmolytic polypeptide (SP). This expanded lineage stained with antibodies against spasmolytic polypeptide (SP), a trefoil peptide secreted from mucous neck cells in the normal fundic mucosa (Wang, et al. (1998); Thim, L. FEBS Lett. 250, 85-90 (1989)). Importantly, the H. felis-induced SP-expressing metaplastic (SPEM) lineage did not show morphological characteristics of mucous neck cells, but rather demonstrated morphology more reminiscent of Brunner""s glands of the duodenum (Wang (1998)).
Given the results in mice, studies were designed to investigate whether H. pylori infection would induce a similar aberrant SP-expressing lineage in human fundic mucosa. Given the epidemiological association of Helicobacter sp. infection with gastric cancer, it was hypothesized that this SP-expressing metaplastic (SPEM) lineage may represent a precursor to or appear commensurate with gastric adenocarcinoma.
The results of these studies showed that the SPEM lineage was present in 65% of fundic biopsies from patients with fundic H. pylori-associated gastritis, but was absent in biopsies of fundic mucosa from patients without H. pylori infection. In a review of archival samples from 22 resected gastric adenocarcinomas, the SPEM lineage was found in 91% of cases, typically located in mucosa adjacent to the carcinoma or areas of dysplasia. Importantly, 56% of samples showed SP immunoreactivity within dysplastic cells. These data indicate not only a strong association between the SPEM lineage and gastric adenocarcinoma, but that SPEM cells represent the metaplastic lineage responsible for development of this tumor in patients with H. pylori.